The present invention relates to a supercharging device arranged between the left and right banks of a V-engine and mounted on the upper surface of a cylinder head.
As a conventional supercharging device, one shown in FIGS. 1 to 5 of Japanese Patent Laid-Open No. 10-103073 (reference 1) is typical. The supercharging device described in reference 1 has a rotor housing accommodating a pair of rotors parallel to the crank shaft of a V-engine. The rotor housing has an intake port open to the rear side and connected to a throttle chamber, a discharge port open to its upper portion, and a bypass channel through which part of the pressurized air discharged from the discharge port is circulated to the intake port. A butterfly valve operated by an actuator is provided to a bypass intake port.
In the conventional supercharging device, a plurality of suction pipes are arranged to surround the side portion of the rotor housing, and the rotor housing and suction pipes are formed integrally. A collector housing is placed over the upper portion of the rotor housing where the discharge port and the suction flow inlets of the suction pipes are formed. The collector housing and suction pipes are fixed integrally with a plurality of bolts. A collector cover is placed over an opening in the upper portion of the collector housing, and is fixed to it.
In the conventional supercharging device having the above arrangement, power transmitted through a pulley and gear box rotates a pair of rotors in the rotor housing in synchronism with each other in opposite directions. The intake air drawn through the intake port is pressurized and discharged into the collector housing through the discharge port, flows through the suction pipes, and is supplied to the suction ports of a cylinder head.
The supercharging device shown in FIGS. 8 to 10 of reference 1 has a rotor housing, a suction pipe, and a collector housing having left and right collectors. The supercharging device also has a pair of cores accommodating intercoolers (heat exchangers) respectively, a cooler housing having discharge ports formed in the two sides of the rear portion and two sides of the front portion, and bypass pipes through which the discharge ports of the cooler housing and the left and right collectors communicate with each other.
In the conventional supercharging device having the above arrangement, the pressurized intake air discharged from the discharge port of the rotor housing flows into the cooler housing through a bypass pipe formed in the collector housing, and is cooled as it flows through the left and right intercoolers. The cooled pressurized air is distributed into the left and right collectors in the collector housing through the bypass pipe, and is supplied to the suction port of the cylinder head from the respective suction pipes.
When a bypass valve is opened by a bypass opening/closing actuator, part of the pressurized intake air discharged from the discharge port of the rotor housing flows through the bypass channel in the collector housing and is introduced to the intake port side of the rotor housing from the bypass intake port. Thus, the supercharging pressure of the discharge port side is adjusted.
In an engine having a supercharging device, as described in, e.g., Japanese Patent Laid-Open No. 2001-82160 (reference 2), a secondary air pipe is attached to the downstream of the supercharging device. Part of the pressurized intake air is supplied to the respective exhaust ports through an air channel formed in the cylinder head. Thus, no air pump for purifying the exhaust gas is required.
In the supercharging device described in reference 1, the rotor housing is formed inside the suction pipes. Thus, when the suction pipes integrally formed with the rotor housing by aluminum alloy casting are mounted on the cylinder head, the vibration of the supercharging device and engine acts on the connecting portion of the rotor housing and suction pipes to form a crack, posing a problem in terms of durability.
In the engine having the supercharging device described in reference 2, the secondary air pipe through which the suction pipe and air channel communicate with each other extends from the side portion to the bottom of the supercharging device. With this piping structure of the secondary air pipe, sometimes the supercharging device cannot be mounted on the cylinder head unless the layout of other auxiliary machinery components is changed.
In the supercharging device described in reference 1, the butterfly valve is built in the bypass channel formed in the rotor housing. Due to the layout of the engine, however, sometimes a space for building in the butterfly valve cannot be formed in the supercharging device. Also, it is difficult to mount the actuator for driving the butterfly valve on the outside of the supercharging device. If the butterfly valve is built in the supercharging device, the number of steps of machining the rotor housing, the number of components of the valve mechanism, and the number of the assembling steps of the valve mechanism increase. Thus, the cost of the supercharging device cannot be decreased.
In the supercharging device described in reference 1, since a suction system channel is formed to distribute the pressurized intake air, discharged from the rotor housing to the collector, into a plurality of suction ports of the cylinder head, the flow of the pressurized intake air to the respective suction ports changes over time. For example, in the case of a V6 engine, the number of suction ports that take air simultaneously is two. More specifically, when a relief valve is built in the conventional supercharging device, as the positive pressure of the collector is not constant, (if the positive pressure and negative pressure are extremely different) an erroneous operation may occur. If the pressurized and heated intake air is introduced to the intake port, the supercharging efficiency decreases.
It is an object of the present invention to provide a V-engine supercharging device in which the durability of the housing is improved.
It is another object of the present invention to provide a V-engine supercharging device that can be mounted on a cylinder head without largely changing the layout of the engine.
It is still another object of the present invention to provide a V-engine supercharging device in which the reliability of the operation of the relief valve is improved.